Holographic displays are means of generating realistic reconstruction of a three-dimensional (“3-D”) object or scene, because they can provide the required depth cues corresponding to the 3-D object or scene exactly. Using holographic techniques, the wave front reflected from an object may be recorded by means of a light sensing device through light interference with a reference wave, or generated based on numerical computation using a suitable numerical model. A recorded wave front may also be reconstructed through light diffraction through use of a spatial light modulator (“SLM”). As a result of such operations, the 3-D object or scene may be regenerated volumetrically at another location.
Holographic information is encoded in the complex amplitude of the light field. Even through complex valued data cannot be directly written on the currently available SLMs, phase-only SLMs or amplitude-only SLMs have been used as dynamic holographic displays. Nevertheless, such SLMs are not yet capable of reaching acceptable performance levels. For example, the space-bandwidth product of commercially available pixelated SLMs is quite small compared to conventional light-sensitive materials used for holographic recording.
Several techniques have been reported for overcoming these obstacles as below.    M. Stanley, M. A. G. Smith, A. P. Smith, P. J. Watson, S. D. Coomber, C. D. Cameron, C. W. Slinger, and A. D. Wood, 3D Electronic Holography Display System Using a 100 Mega-Pixel Spatial Light Modulator, Volume 5249, pp. 297-308, Proc. of SPIE, 2004. [QinetiQ]    J Hahn, H. Kim, Y. Lim, G. Park and B. Lee, Wide Viewing Angle Dynamic Holographic Stereogram With a Curved Array of Spatial Light Modulators, Opt. Express, 16(16):12372-12386, 2008. [Seoul Univ.]    Michael A. Klug, and Mark E. Holzbach, Full-parallax holographic stereograms on curved substrates, U.S. Pat. No. 6,631,016. [Zebra Imaging, Inc.]    Edward Buckley, and Diego Gil-Leyva, Optical systems, United States Patent 2010/0165429. [Light Blue Optics Ltd.]
The QinetiQ approach sequentially employs two SLMs, an electrically-addressed spatial light modulator (“EASLM”) and an optically-addressed spatial light modulator (“OASLM”). The EASLM, which has one million pixels, is used to display synthetic fringe patterns, whereas replication optics is used to magnify and tile onto the OASLM the patterns to be displayed. Through use of an electrical shutter in the optics, each fringe pattern is simultaneously projected on an associated segment of the OASLM at a given time. This system uses a Ferro liquid crystal display (FLCD) whose switching time is much shorter than that of a typical LCD, such as that used as the EASLM. In this way, an output per channel of 26 million pixels has been achieved on a 5×5 matrix of SLMs in an OASLM implementation. The space-bandwidth product is increased through use of the two different SLMs and replication optics. However, such an approach is suitable only for planar configurations due to the geometry of the replication optics; in particular, this approach is not suitable for curved display devices.
A curved display configuration with multiple SLMs based on a holographic stereogram approach has been presented by Lee et al. This system was implemented with twelve SLMs, wherein each SLM had a corresponding transfer lens and two mirror modules that divided the diffracted light from the SLM into three partitions that were then recombined in a form three times wider (although the height of the reformed SLM image was reduced). Therefore, the effective number of SLMs was 36. Their approach was based on a horizontal parallax only (“HPO”) holographic stereogram in which an asymmetric diffuser was used as a screen. Using this method, they achieved a viewing angle of approximately 22.8 degrees with a continuous viewing zone. However, such an approach may not be suitable for commercial applications, because the design of the light illumination optics for multiple SLMs is very complex, and because a cylindrical configuration that has a 360 degree continuous viewing zone cannot be implemented. Furthermore, this technique is not suitable for full parallax holographic display, because of the reduced vertical resolution on the SLM plane. Given these deficiencies of the prior art, there is a need for a SLM-based display device that has a curved configuration.
A holographic stereogram recording method have been reported by Michael A. Klug et al. at Zebra Imaging Inc. so as to display a desired three-dimensional object by a hologram that is mounted on a curved substrate where the hologram is full parallax, one-step recording and full color holographic stereogram. The hologram, which can be mounted on an arbitrary shaped substrate, is partitioned by one or more tiles, and each tile is comprised of one or more holographic elements. A plurality of hogels is recorded on the tile by varying at least one of a holographic element orientation corresponding to a desired three-dimensional object. Therefore, the major advantage of such hologram is that the hologram can be formed in arbitrary shapes due to the hologram tiling and tiles mounting on an arbitrary shaped substrate individually. On the contrary to this, one of the disadvantages of this hologram is that it can display only still three-dimensional image due to the recording of holographic elements on a photo-refractive material.
Even though such approach can provide the three-dimensional representation holographically, it may not be proper for a moving object display for example a holographic-TV and holographic video.
A holographic head up display for displaying an image on a curved surface such as a windshield of a vehicle was presented by Edward Buckley et al. at Light Blue Optics Ltd. The holographic head up display can be comprised of a spatial light modulator (SLM), a projection system, and a computing system. Due to the various shapes of the windshield of a vehicle, the corresponding wave front correction data is recorded in the non-volatile data memory in the computing system as initialization in order to display the image on the curved surface without shape distortion. The desired two-dimensional images and the recorded wave front correction data are used to generate corresponding fringe patterns. The generated fringe patterns are displayed over the SLM, and a plane wave is illuminated over the SLM. The modulated light by the SLM is projected on the curved surface by the projection system. In this system, the holographic techniques are applied to correct the displayed image for aberration or shape distortion due to a shape of a display surface. Therefore, a windshield or other curved surface can be used as an image screen to provide a two-dimensional image holographically to an observer. However such system can be applicable to only two-dimensional image display on a curved surface. In other words, the presented system may not be suitable to display a three-dimensional object in a space and its viewing angle is also restricted by the projection system.